This invention relates to a system for controlling flow of current to and dissipating energy from a D.C. motor connected to the output of a rectified A.C. or D.C. supply source.
The Moscardi U.S. Pat. No. 3,250,978 discloses a system for controlling the flow of energy to and from a D.C. motor connected to a D.C. supply having substantially a constant potential, such as provided by a battery or rotary D.C. generator. In Moscardi the motor armature circuit is connected between the low potential side of the source and the center tap of an inductor which is connected at both of its ends through controllable electronic devices to the opposite sides of the source. By suitable oscillator based control means in circuit with the electronic devices and by use of capacitors connected between the opposite sides of the source and the tap of the inductor, the electronic devices can be switched on-and-off in an alternate manner to provide a "chopper" type of current control in the motor armature circuit. Diodes connected in parallel with the capacitors and poled in a direction opposite the direction of current flow in the electronic devices permits continued armature current flow when no energy is being supplied from the source, and also affords pump-back of energy to the source under overhauling conditions of motor operations.
The control of the electronic devices of Moscardi is of the open-loop type which precludes close control of speed deviation under changing loads. Moreover, it cannot be used with a rectifier, A.C. to D.C. type of supply if the motor is subjected to overhauling loads of any appreciable magnitude and duration.